1. The Field of the Invention
This application is directed to compositions which are particularly useful in dentistry. More particularly, this application is directed to two-part, temporary dental cements.
2. The Relevant Technology
Dental cements are well known in the art. Permanent dental cements are typically employed to adhere a dental appliance or prosthesis to a tooth which has been prepared to receive the prosthesis or appliance. Modern permanent dental cements are typically comprised of a powder/liquid mixture comprising: (i) a first component, or component "A," such as zinc oxide or glass ionomer silica; and (ii) a second component, or component "B," such as an aqueous solution of polyacrylic acid or phosphoric acid.
With the mixture of zinc oxide and aqueous polyacrylic acid, for example, an acid-base reaction occurs which forms a salt. The salt has a matrix which forms a strong bond between (i) a tooth; and (ii) a prosthesis or appliance. Typical permanent dental cements are also resistant to erosion in oral fluid and feature a low irritancy to tooth pulp.
When resins are employed as a permanent bonding material, the deposition of the final permanent bonding material is typically preceded by the application of a hydrophilic resin primer(s) to the tooth preparation. Bonding primers bond to the tooth surface, after which the permanent luting resin is bonded onto the bonding primer. The use of a bonding primer increases the overall adhesion of the permanent luting resin cement.
Although permanent dental cements are highly useful for a variety of different dental purposes, it is usually necessary to temporarily affix a prosthesis or appliance to a tooth, then later remove the prosthesis or appliance. For example, before mounting a permanent crown on a tooth which has been prepared to receive the crown, a dentist typically makes an impression of the tooth. The dentist then mounts a temporary crown on the tooth and sends the impression to a laboratory for manufacture of the permanent crown.
The temporary crown is held in place by a temporary dental cement until the permanent crown is prepared, upon which the temporary crown is removed. The permanent crown is then permanently affixed to the tooth through the use of permanent dental cement. Typical temporary dental cements are comprised of eugenol, rosins, pine gums, or tall oil mixed with zinc oxide.
Removal of temporary crowns from teeth is generally significantly easier than removal of permanent crowns from teeth due to the use of temporary dental cement, which is significantly weaker than permanent dental cement. Nevertheless, certain problems are associated with temporary cements currently used in dentistry.
For example, typical two-part temporary dental cements leave an insoluble, oily residue on a tooth and/or contaminate the underlying dentin and/or enamel so as to preclude quality definitive bonding, such as luting or another form of cementation. In addition to the annoyance of the film residue, the residue or contaminant on the tooth can contaminate a subsequent permanent bonding attempt because of incompatibility between the temporary cement contaminant and a bonding material placed on the residue, such as a bonding primer. The incompatibility between the residual temporary cement and the subsequently applied primer can interfere with the bonding of a permanent luting resin or another cement to the tooth.
This incompatibility is often caused by hydrophobic components within typical temporary dental cements which are incompatible with hydrophilic bonding materials, such as dental bonding primers, which are typically hydrophilic, at least upon initial placement upon the tooth surface before the primer is cured. Hydrophobic temporary cements which leave a residue on the tooth contaminate the bonding surface for the hydrophilic primers or other hydrophilic bonding materials. In addition, even some hydrophobic resins are caused not to polymerize by some hydrophobic temporary cement residues.
As a further complication, it is also often difficult to clean up typical hydrophobic temporary cements. These cements must generally be cleaned off with another hydrophobic composition, such as oil of orange, or another hydrophobic cleaner. Furthermore, typical hydrophobic temporary cements, such as eugenol, can also be irritating to nerve and pulp tissue.
Finally, typical temporary cements do not form a chemical bond with a dental substrate, but rather, use mechanical methods to retain a crown, for example, on a dental substrate. Consequently a drilled tooth cavity, for example, is suseptible to contamination and leakage of bacteria and other microorganisms into the cavity while the temporary cement is placed therein.
There is therefore a need in the art for an improved temporary dental cement. More specifically, there is a need in the art for a temporary dental cement which does not interfere with the bonding of a primer or permanent cement placed on a tooth after the removal of a temporary prosthesis or appliance from the tooth. There is also a need in the art for a temporary dental cement which readily cleans from a tooth, which does not irritate nerve and pulp tissue, and which does not permit microleakage of bacteria.